Aquarium Nitrogen Cycle

Three Main Chemical Compounds

Full tank shot of planted aquariumFirst, lets look at each of the three main chemical compounds that are present in the Aquarium Nitrogen Cycle.

Ammonia: Also known as unionized Ammonia (NH3). This toxin is released into your aquarium water from fish waste, uneaten food, or a fish that dies in the tank. This is a very dangerous toxin that can lead to ammonia poisoning which could kill your fish.

Ammonium (NH4) is the chemical compound that is released just as Ammonia, but it is much less harmful than Ammonia. Ammonium actually turns into Ammonia when your pH is higher than 7.

Nitrite: - (NO2) This chemical compound is created when the poisonous Ammonia is broken down in your aquarium water. Nitrite is a toxin and can kill your fish if levels are not kept under control.

Nitrate: - (NO3) Nitrates are the product of Nitrites being broken down in your aquarium. Nitrates are the least toxic to your fish. Although they are less toxic, large amounts of nitrates can still harm your fish. Nitrates are eventually broken down and converted into Nitrogen Gas.

The Aquarium Cycle Process

This process is known as the aquarium cycle, fish tank cycle, or aquarium nitrogen cycle. You will hear people talking about cycling a new aquarium or tank cycling. These terms all mean the same thing.

This process involves 3 steps and usually averages 4-6 weeks to complete.

The first stage: (2-3 weeks)

Fish will produce waste like any living organism. Tropical fish keepers also may contribute by not properly cleaning the tank, overfeeding, or keeping too many fish in one tank. These waste products are converted into ammonia as they are being broken down. If there is not enough nitrosomonas bacteria established in your aquarium, ammonia can build up and kill your fish by ammonia poisoning.

Under normal or average conditions, it takes 2-3 weeks for enough beneficial bacteria to build up and effectively break down ammonia into nitrite. Up to this point, you should have significant Ammonia readings in your test results.

Be patient and do not add any fish to the tank. High amounts of ammonia burn the gills, tissue, and eventually kill the fish.

The second stage: (2 weeks)

At this stage the tropical fish tank needs to have substantial amounts of beneficial bacteria in the substrate, water column, or biological filter media. This will allow for proper conversion of ammonia to nitrite.

Nitrite will stay in your water column until it is broken down by beneficial bacteria or reduced through water changes.

Up to this point, it is normal to still show some Ammonia in your water and significant amounts of Nitrite when you perform you aquarium water tests.

Again, high nitrite levels can kill your fish.

The third stage: (1-2 weeks)

At this point, there should be an established beneficial bacteria colony in your aquarium. This bacteria should be converting the toxic nitrite into less harmful nitrate.

When testing your water you may show a little nitrite, but this should decrease as your beneficial bacteria colony grows. You should have moderate levels of nitrate at this point.

Keeping live plants and regular water changes will reduce the amount of nitrates in your aquarium tank.

All three of the chemical compounds (ammonia, nitrite, and nitrates) are naturally going to be found in an occupied tropical fish tank. Nature can do its part, but we tropical fish keepers must do our part also to help reduce the toxins in our tropical aquarium tank.

There are a number of products (in which I will share with you soon) that can help lower ammonia, nitrites, and nitrates. These are especially good to use in emergency situations when you have a significant build up in one or more of the above-mentioned chemical compounds.

The best thing you can do to keep nitrates or the other two above-mentioned compounds under control is regular water changes. Clean, fresh water will help keep your nitrate level down and your tropical fish happy and healthy.

Tips to reduce Ammonia,
Nitrite, and Nitrate

  • Increase your biological filtration.
  • Do not overfeed.
  • Do not overstock your aquarium.
  • Increase water changes.
  • Monitor for dying plants or dead fish.
  • Vacuum your aquarium gravel during every water change. Vacuum in sections. Do not vacuum the entire tank all at once; this can deplete your beneficial bacteria.

Summary of the Aquarium Nitrogen Cycle

  1. Fish waste and other pollutants are released in the aquarium water.
  2. Ammonia is created from the waste products.
  3. Ammonia is broken down by nitrosomonas bacteria and converted into Nitrites.
  4. The beneficial bacteria then break down nitrites and this creates Nitrates.
  5. Nitrates are in the water until live plants absorb them, removed through water changes, or eventually broken down into nitrogen gas by the beneficial bacteria in your aquarium water.

The Aquarium Nitrogen Cycle is easily maintained once it is initially established. Excellent water quality through the above mentioned steps will ensure you have happy, thriving, healthy tropical fish.


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